1. Field of the Invention
The present invention relates to a structure for a slip ring and a brush of a wound rotor synchronous motor (WRSM), and more particularly, to a structure for a slip ring and a brush of a WRSM capable of reducing an axial length of a motor by increasing a contact area between the slip ring and the brush and improving reliability for smoothly implementing performance of the motor by stably supporting a shaft of the motor.
2. Discussion of Related Art
In general, a hybrid car or an electric car that has been mentioned as an eco-friendly car, is driven by an electric motor that obtains a rotational force using electric energy.
The hybrid car drives in an electric vehicle (EV) mode that is a pure electric car mode in which only power of the electric motor is used, or in a hybrid electric vehicle (HEV) mode in which both an engine and a rotational force of a driving motor are used as power. The conventional electric car drives using the rotational force of the driving motor as power.
In this way, the driving motor used as a power source for the eco-friendly car is usually a permanent magnetic synchronous motor (PMSM). The PMSM is required to maximize performance of a permanent magnet so as to show the maximum performance on a limited layout condition.
Here, neodymium (Nd) in the permanent magnet is used to improve an intensity of the permanent magnet, and dysprosium (Dy) is used to improve a high-temperature demagnetization resistance. However, rare-earth metals in the permanent magnet, such as Nd and Dy, are limitedly buried in some countries including China, etc. and are very expensive and have severe price fluctuation.
In order to overcome these disadvantages, the use of an induction motor has been examined. However, there is a limitation in excessive increment in sizes, such as volume, weight, and the like, so as to show the same motor performance.
Meanwhile, in related industry, development for a wound rotor synchronous motor (WRSM) that replaces a PMSM as an electric motor used as the power source for the eco-friendly car has been more briskly carried out.
The WRSM is capable of showing performance of a motor with an optimal increase of about 10% compared to the PMSM. The WRSM replaces a permanent magnet of the PMSM by winding a coil around a rotor and making the rotor in a state of an electromagnet when a current is applied to the coil.
The WRSM is configured in such a way that a coil is wound around the rotor so as to generate a magnetic flux in the rotor and a brush and a slip ring are provided outside a housing of the motor so as to generate a magnetic flux by flowing a current through the coil and the current is applied to the coil through the brush and the slip ring.
Meanwhile, the WRSM is configured in such a way that the brush is always maintained in mechanical contact with an outer circumferential surface of the slip ring so that a direct current (DC) is applied to the wound coil, and for continuous mechanical contact between the brush and the slip ring, an end of one side of the brush is elastically supported by a spring and the brush is maintained in a continuous contact state with the outer circumferential surface of the slip ring due to an elastic force of the spring and a current is transferred to the coil.
However, in the conventional structure for a slip ring and a brush of a WRSM, a contact area between the slip ring and the brush for applying a DC is relatively small compared to the entire area of the slip ring such that a contact resistance increases when a high current is input to the coil through the brush and thus, heat dissipation and loss occur in the motor. Also, friction and abrasion occur in the contact surface due to repetitive mechanical contact between the brush and the slip ring, and due to such friction and abrasion, foreign substances, such as metal powder, are formed such that a spark, etc., occurs and the durable reliability of the motor is lowered.
Furthermore, when the slip ring extends in an axial direction and the axial length of the slip ring is increased so that a sufficient contact area between the brush and the slip ring is obtained, the contact area between the slip ring and the brush is increased but, due to an increase in the axial length of the slip ring, the size of the motor may be excessively increased.